Radial secondary gas flow carbon black reaction method

ABSTRACT

A method is provided for producing a carbon black with a tint residual below -6. The method entails introducing feedstock axially and generating a hot combustion gas vortex in a cylindrical precombustion section of a tubular carbon black reactor, producing a first mixture of feedstock and combustion gases, passing the mixture through an abruptly restricted passage axially connected to the precombustion section, abruptly expanding the first mixture into a frustoconical venturi converging section of the reactor with mixing of this first mixture with an additional flow of combustion gas at the exit of the converging section with the combustion gas entering the converging section in opposite, radial flow thereby forming a second mixture which is admitted into a reaction section of the carbon black reactor.

This application is a division of copending application Ser. No.718,301, filed Aug. 27, 1976, now allowed, U.S. Pat. No. 4,127,387.

BACKGROUND OF THE INVENTION

This invention relates to the production of carbon black. In one of itsaspects this invention relates to the production of carbon black with atint residual below -6. In another of its aspects this invention relatesto carbon black reactors.

It is important to reduce the heat buildup, also called hysteresis, orrubber/carbon black compositions. Hysteresis is a measurement of howmuch of the elastic deformation energy put into a carbon black/rubbercomposition remains in the composition as heat after the deformationforces have been released. Serious accidents have been attributed to thefailure of tires made from high hysteresis rubber compositions. Thehigher the heat buildup in the rubber compositions the greater are thechances the tires made from such compositions can be destroyed in use.

It has recently been set forth in copending application, Ser. No.681,977, filed Apr. 30, 1976, now U.S. Pat. No. 4,071,496, incorporatedherein by reference, that a rubber composition exhibiting low heatbuildup along with satisfactory tread wear properties is provided in acomposition comprising 100 parts by weight of rubber and 30 to 120 partsby weight of a carbon black having a tint residual of about -6 or less.Tint residual is a property of carbon black defined by the followingformula:

    TR=T-[56.0+1.057(CTAB)-0.002745(CTAB).sup.2 -0.2596(DBP)-0.201(N.sub.2 SA--CTAB)].

In this formula, the abbreviations used have the following meanings andthe properties are measured as described:

TR: This is the tint residual.

CTAB: This is the surface area of the carbon black measured as describedby J. Janzen and G. Kraus in Rubber Chemistry and Technology, 44, 1287(1971), m² /gm.

N₂ SA: This is the surface area of the carbon black measured usingnitrogen in accordance with the ASTM method D-3037-71T, m² /gm.

DBP: This is the structure of the carbon black in cc/100 g and ismeasured in accordance with U.S. Pat. No. 3,548,454 and, after crushing,by method B in accordance with ASTM D-2414-70. This property is alsoreferred to as 24M4 DBP.

T: This is the tint or tinting strength of the carbon black measured byarbitrarily assigning the reference black IRB No. 3 the value of 100;the tint is measured in accordance with ASTM 3265-75.

It is therefore an object of this invention to provide an apparatussuitable for preparing carbon black having a tint residual of -6 orless. It is another object of this invention to provide a method forproducing carbon black having a tint residual of -6 or less.

Other aspects, objects, and the various advantages of this inventionwill become apparent upon study of this specification, the drawings, andthe appended claims.

STATEMENT OF THE INVENTION

According to this invention an apparatus is provided for the preparationof carbon black. In this apparatus, described as a tubular carbon blackreactor, is a cylindrical precombustion section having axially alignedinlet for feedstock and means for generating a hot combustion gasvortex. The precombustion section is axially aligned and openlyconnected in operative communication with a passage of abruptlyrestricted dimensions, with this passage in further axial alignment andopenly connected in operative communication with a frustoconical,venturi converging section which abruptly expands from the passage to adiameter equal to that of the precombustion section. The venturiconverging section extends away from the passage at a converging angleof about 10 to about 30 degrees between the frustoconical surface andthe reactor axis and the converging section terminates openly connectedin operative communication with an axially aligned reaction tube sectionwhich has a diameter equal to the least diameter of the convergingsection. In the converging section at the inlet to the reaction tubesection are means for introducing radial and opposing streams ofcombustion gas into the reactor. The mixing action resulting from theplacement of the entry of radially, opposing combustion gas streams intoa reactor capable of producing a well mixed flow of combustion gas andcarbon black feedstock will be shown herein to contribute to theproduction of carbon black having a low tint residual.

In accordance with another embodiment of the invention a method isprovided for producing carbon black having a tint residual of about -6or less in which carbon black feedstock is axially passed into acylindrical precombustion section of a carbon black reactor while avortex of hot combustion gas is generated in the precombustion sectionthereby producing a first mixture of feedstock and combustion gases thatis passed from the precombustion section axially through an abruptlyrestricted passage and abruptly expanded. The expanded mixture then ispassed through a frustoconical venturi converging section therebyconverging the axially flowing mixture and at the exit of the convergingsection mixing the first mixture with radial, opposite flow ofcombustion gas to form a second mixture. Carbon black is then producedfrom the second mixture in a confined reaction section of the carbonblack reactor.

The invention can best be understood in conjunction with the drawing inwhich:

FIG. 1 is a cut-away view of a carbon black reactor of the presentinvention and;

FIG. 2 is a cut-away view of a carbon black reactor of the prior art.

In the FIGURES the reactors are identical with the exception of thelocation of the entry for supplemental combustion gas in thefrustoconical, venturi converging section. In FIG. 1 this supplementalcombustion gas is supplied by opposing radial tubes preferably locatednear the outlet of the converging section and in FIG. 2, which depictsthe prior art apparatus, the supplemental combustion gas is suppliedtangentially into the converging section, preferably in the portionhaving the greatest diameter where a mixture of gases has been abruptlyexpanded into the venturi converging section of the reactor.

Referring now to FIG. 1 or FIG. 2, like numbers will be used todesignate portions of the apparatus that are duplicated in the twoFIGURES. Feed enters with axial flow through inlet means 1 to be mixedin a cylindrical precombustion section 3 with combustion gases fed intoprecombustion section 3 through tangential inlet means 5 so that theaxially flowing feedstock is mixed with a vortex of hot combustion gasesto form a first mixture of feedstock and combustion gases. The firstmixture then flows through a passage of abruptly restricted dimensions 7which is axialy aligned with both the feedstock inlet and thecylindrical precombustion section. The first mixture is discharged intoa frustoconical, venturi converging section 9 which abruptly expands toa diameter equal to that of the precombustion section 3. The convergingsection 9 extends away from the restricted passage 7 at a convergingangle of about 10 to about 30 degrees between the frustoconical surface11 and the axis of the reactor 13. The converging section 9 terminatesin open communication with an axially aligned reaction tube section 15which has a diameter equal the least diameter of the converging section.

Apparatuses for the production of carbon black constructed as describedabove are well known in the art. Also known is the introduction ofsupplemental combustion gases through tangential flow means 17 locatedin the venturi converging section 9. In the present inventionsupplemental combustion gas is introduced into the venturi convergingsection 9 through opposed, radial flow means 19 preferably located nearthe termination of the converging section 9 into the reaction tube 15.

The dimensions of the reaction apparatus according to this invention canrange from a cylindrical precombustion section having a diameter about 4inches up to about 40 inches and an axial length from about 3 inches upto about 12 inches with the length shorter than the diameter. Dependingupon the dimensions of the precombustion section the abruptly restricteddimensions of the outlet passage will range from about 1/2 inch up toabout 16 inches in diameter. The converging section will generally haveits greatest diameter equal to that of the precombustion section and asit extends away from the restricted passage connecting it to theprecombustion chamber will converge at an angle ranging from about 10 toabout 30 degrees with the angle measured between the frustoconicalsurface of the converging section and the axis of the reactor. Thereactor section will generally range from a diameter of about 1/2 inchup to about 8 inches. The inlet lines for reactor feedstock andcombustion gases can be sized according to the flow that these passagescarry.

In the following examples, reactor blocks were used in which the feedinlet 1 was a 1/2 inch diameter 4-inch line, the cylindricalprecombustion section 3 was 3 inches long and had a diameter of 4inches, tangential combustion gas inlets 5 were 1/4 inch diameter, theabruptly restricted passage 4 was 1 inch long and of cross-section of anequilateral triangle circumscribed about a 1/2 diameter circle, theconverging section 9 was about 4 inches long with the coverging angle ofabout 24 degrees, the reaction tube 15 was about 1/2 inch diameter andboth the opposed radial, supplemental combustion gas inlets 19 of thisinvention and the tangential, supplemental combustion gas inlets 17 ofthe prior art were about 1/4 inch in diameter. Flow rates and propertiesof the carbon black product produced in the various runs are describedbelow in Table I.

                                      TABLE I                                     __________________________________________________________________________                    Invention Runs                Control Runs                    Run Numbers:    1    2    3    4    5    6    7    8                          __________________________________________________________________________    Axial Benzene.sup.1, cc/min.,                                                                 5.75 8.0  15.5 17.2 17.2 19.2 14.5 13.0                       Cylindrical Zone:                                                             Tangential Air, SCF/min.,                                                                      3.96 for all eight runs                                      Tangential Methane, SCF/min.,                                                                  0.314 for all eight runs                                     Volume ratio Air to Fuel,                                                                     12.6/1 for all eight runs                                     __________________________________________________________________________    Converging Zone:                                                                              Equal Flow Opposing Jet       Tangential                      __________________________________________________________________________    Air, SCF/min.,  0.30 2.27 2.27 2.27 2.27 2.27 2.27 2.27                       Methane, SCF/min.,                                                                            0    0.10 0.10 0.10 0.10 0.10 0.10 0.10                       Volume ratio Air to Fuel,                                                                     --   22.7 22.7 22.7 22.7 22.7 22.7 22.7                       Carbon Black Product:                                                         CTAB, m.sup.2 /gm.,                                                                           154  112  83   67   70   62   65   63                         N.sub.2 SA, m.sup.2 /gm.,                                                                     182  127  96   68   74   63   65   63                         I.sub.2 No., m.sup.2 /gm.,                                                                    159  120  89   64   69   55   61   62                         24M4 DBP, cc/100 gm.,                                                                         90   86   83   80   84   86   91   88                         Tint,           115  102  87   79   80   76   75   78                         Tint Residual,  -10  -13  -14  -14.5                                                                              -13.5                                                                              -12  +14  +11                        Photelometer Value,                                                                           --   96   95   90   93   88   86   92                         Grams Product/30 min.,                                                                        37.0 26   58   79   93   90   58   83                         __________________________________________________________________________     .sup.1 Oil outlet at upstream face of first (cylindrical) zone.          

It will be noted that the tint residual of the carbon black productproduced using the apparatus and method of this invention all fell in arange below -6 while the product of the control runs had a tint residualin a range well above -6.

We claim:
 1. A method for producing carbon black having a tint residualof about -6 or less, said method comprising:(a) axially passingfeedstock into a cylindrical precombustion section of a carbon blackreactor while generating a vortex of hot combustion gas in saidprecombustion section to produce a first mixture of feedstock andcombustion gas; (b) passing said first mixture axially from saidprecombustion section through an abruptly restricted passage; (c)abruptly expanding said first mixture; (d) converging the axiallyflowing mixture; (e) mixing said converging first mixture with radial,opposite flow of combustion gas to form a second mixture; and (f) in aconfined reaction section producing carbon black from said secondmixture.
 2. A method of claim 1 wherein radial, opposite flow ofcombustion gas is substantially equal in volume.
 3. A method of claim 1wherein said mixing of converging first mixture with radial, oppositeflow of combustion gas occurs as the converging mixture is near theinlet of the confined reaction zone.